The invention is directed to a prismatic capacitor, particularly to a very thin capacitor. The invention is particularly useful with electrolytic capacitors and especially with hybrid capacitors combining characteristics of electrochemical and wet slug capacitors.
Wet slug capacitors typically employing anodes made from valve metals bearing an oxide coating of the valve metal are well known. These conventional wet slug electrolytic capacitors are available in numerous sizes, both in terms of physical size and shape, the traditional shape being cylindrical. The anodes of typical wet slug capacitors are usually one of tantalum, aluminum, niobium, zirconium, or titanium, all metals that form a native oxide and in which the native oxide can be electrolytically increased in thickness. These wet slug capacitors have relatively high breakdown voltages but their energy storage density is relatively low.
Another kind of capacitor, typically referred to as an electrochemical capacitor, employs electrodes of porous metal oxides with the metal usually selected from the group consisting of ruthenium, iridium, nickel, rhodium, platinum, palladium, and osmium. These electrochemical capacitors have relatively high energy storage densities but relatively low breakdown voltages.
The advantages of wet slug capacitors and electrochemical capacitors can be combined to provide capacitors with relatively high breakdown voltages and relatively high energy storage densities, as described in U.S. Pat. Nos. 5,369,547, 5,469,325, and 5,754,394, the disclosures of which are incorporated herein by reference. Examples of such capacitors having various shapes, including cylindrical and relatively flat capacitor cells, are disclosed in those patents. Typically, in the flat or cubic capacitors, mutually electrically isolated electrodes are disposed at opposite sides of the capacitor package with, possibly, an anode between the electrodes. Assembly of those flat capacitors requires bonding of numerous elements and an insulating seal impervious to an electrolyte between the two electrodes. The complexity of these capacitors complicates their assembly and increases their cost.
It is an object of the present invention to provide a thin capacitor that is relatively flat, yet provides high energy storage density, high breakdown voltage, and is simple in construction and low in production cost.
It is a further object of the invention to provide a method of making such a capacitor.
A capacitor according to the invention includes a generally planar anode having two opposed faces, a lead wire, and a resilient body surrounding a part of the lead wire; an ion-permeable separator wrapped around and contacting the faces of the anode, the lead wire protruding through the separator; an electrolyte permeating the separator; and a one-piece metal foil case including at least one recess having an inside surface coated with a coating for forming a capacitor with the anode, the coating being in contact with the separator, the metal foil having a fold along one side of the capacitor that contains a hole in which the resilient body is disposed in a liquid-tight seal with the metal foil case, and peripheral parts extending around the case from the fold and that include a sealed seam of surfaces of the metal foil, hermetically sealing the electrolyte, the separator, and the anode within the metal foil case.
A method of making a capacitor according to the invention includes providing a metal foil blank having an inside surface, an outside surface, and at least one edge; forming two substantially similar recesses on the inside surface of the metal foil blank, leaving a peripheral flange surrounding the recesses at the edge of the metal foil blank; before or after forming the recesses, coating the inside surface of the metal foil with a coating for forming an electrode of a capacitor; before or after applying the coating, forming a hole in the metal foil blank spaced from the edge and between the two recesses; placing an ion-permeable separator on the inside surface of the metal foil blank; before or after placing the ion-permeable separator on the inside surface of the metal foil blank, adding an electrolyte to the separator; preparing an assembly of a substantially planar anode having an area no larger than the area of the two substantially similar recesses and a lead connected to the anode; inserting the lead through the separator and the hole; placing a resilient body on and surrounding part of the lead proximate the anode and inserting the body into the hole in the metal foil blank; folding the metal foil blank along a line intersecting the hole and lying between the two recesses so that the anode is sandwiched between the separator and the separator is in contact with the coating on the inside surface of the metal foil in the recesses, bringing parts of the peripheral flange of the metal foil blank into contact with each other; and sealing the parts of the peripheral flange of the metal foil blank that are in contact with each other to form a hermetically sealed metal foil case.